Secretary of State John F. Kerry (third from right at the table) speaks about Russian involvement in Syria during a U.N. Security Council meeting on Sept. 21. (Justin Lane/European Pressphoto Agency)

Secretary of State John F. Kerry called on Russia and Syria on Wednesday to “immediately ground all aircraft” flying in key areas of northwest Syria where a humanitarian convoy was destroyed Monday, and accused Moscow of inventing its “own facts” to explain the air attack for which Russia is responsible.

“The simple reality is we cannot resolve this crisis if major parties . . . are unwilling to do what’s necessary to avoid escalation,” Kerry told the U.N. Security Council. “We don’t get anywhere by ignoring facts and denying common sense.”

Kerry’s caustic intervention came after Russian Foreign Minister Sergei Lavrov denounced “emotional reactions” to the strike on the convoy and called for a “serious” investigation of the incident. After suggesting that the attack was perpetrated by terrorist ground forces­ active in the area southwest of Aleppo, Moscow newly implied that it could have been a U.S. drone.

Amid the charges and counter­charges, speakers to the council pleaded for cooperation that could lead to a genuine cease-fire in the five-year civil war, and excoriated the international community as a whole for not ending the carnage.

“The Syrian tragedy shames us all,” U.N. Secretary General Ban Ki-moon said in opening the meeting. “The collective failure of the international community should haunt every member of this council.”

The meeting, called by New Zealand, the current council president, was not on the official schedule but was tacked on to a session called to discuss the recently completed peace agreement in Colombia. Kerry, Lavrov and other foreign ministers quickly took over the chairs that had been occupied by their U.N. ambassadors.

But while all bemoaned the ongoing strife in Syria, agreed that the crumbling cease-fire was the only way out and pledged to do better at implementing it, attention was focused on the sharp exchange between Kerry and Lavrov. In remarks Kerry described as a “parallel universe,” Lavrov said that one of the clearest violations of the cease-fire the United States and Russia agreed to nearly two weeks ago was “the Sept. 16 attack by the [U.S.-led] coalition against government forces” — the apparently mistaken airstrike in eastern Syria that killed dozens of Syrian soldiers.

The convoy attack Monday, Lavrov said, was “another unacceptable provocation,” which took place west of Aleppo near forces­ of the Front for the Conquest of Syria, the al-Qaeda affiliate formerly known as Jabhat al-Nusra. “On the same day, in the same area, there was a very aggressive attack against government ­forces,” he said. “These kind of coincidences require serious analysis and investigation. . . . Many said [the convoy attack] could have been a rocket or a mortar.”

He said Russia had presented proof, “including real-time video of when this actually happened.”

In Moscow, the Defense Ministry said Wednesday that a coalition Predator drone, which it said had taken off from Incirlik air base in Turkey, was seen near the route of the convoy on the day of the attack. Russia has said repeatedly that no Russian or Syrian aircraft was in the vicinity.

The drone “was spotted in midair at the height of 3,600 meters, moving at the speed of about 200 kilometers an hour, exactly in this area on September 19,” Maj. Gen. Igor Konashenkov, a Defense Ministry spokesman, told reporters at a briefing. The drone, he said, “stopped near the area of the populated locality of Urum al-Kubra,” where the strike took place “several minutes before the convoy caught fire. And it left about 30 minutes later.”

“This type of drone not only can observe the situation, but also direct ground weapons and autonomously deliver high-accuracy strikes on secure facilities,” Konashenkov said.

Capt. Jeff Davis, a Defense Department spokesman, said in an emailed statement, “We can confirm that NONE of our aircraft — manned or unmanned, US or Coalition — were anywhere in the vicinity of Aleppo when the strike against the humanitarian convoy occurred.”

Kerry also replied scornfully to Lavrov’s description of the attack. “I don’t think we can let anybody here, if we’re going to deal with this situation, have their own set of facts about Syria,” he said. “Twenty aid workers were killed in an outrageous, sustained, two-hour attack directed at a fully authorized humanitarian mission near Aleppo.”

Pentagon officials have said their “preliminary” conclusions are that the convoy was hit by a Russian airstrike. Those conclusions, he said, have been supported by some activists and other humanitarian groups. But the International Committee for the Red Cross said it could not confirm the source of the attack.

Just Tuesday night, Kerry said, there were “reports of airstrikes on a medical facility near Aleppo, and four medical workers were killed, despite the fact there is supposed to be a cessation. There are only two countries that have airplanes that are flying during the night or flying at all in that particular area: Russia and Syria.”

“Yes, the coalition did hit people on Saturday,” Kerry said. “We did it. It was a terrible accident. Within moments of it happening, we acknowledged it. We didn’t put out a bunch of obfuscating facts. We said, ‘Yeah, it’s a terrible thing, it happened.’ The Defense Department apologized, and we tried to find out how it happened.”

But the view from the air of “people running around with guns on the ground . . . is a different thing from trucks in a convoy, with big U.N. markings all over them,” Kerry said.

Kerry’s proposal to ground all aircraft in the northwest area around Aleppo, where government forces­ and their Iranian and Hezbollah allies are present along with moderate opposition and jihadist ­forces, is a significant change from the original terms of the U.S.-Russia agreement. It imposed no initial restriction on Syrian airstrikes against Front ­forces, while saying that once a cease-fire against all but terrorist groups was holding and aid was being delivered, the United States and Russia would take over with exclusive responsibility for strikes against the Front and the Islamic State.

In his remarks, Lavrov repeated Russia’s insistence that the deal also called for the United States and its allies supporting the opposition to separate rebel forces­ from nearby jihadist groups. “In spite of our appeals on the need to influence the armed opposition,” he said, “so far the results have been very insignificant.”

Kerry acknowledged that “for too long some elements of the opposition have relied on an unholy coalition with al-Nusra. . . . Al-Nusra is al-Qaeda,” he said. “We can’t look the other way if groups on the ground are fighting with . . . an enemy of all in this room.”

But, he said, “it’s very hard to separate people when they are being bombed indiscriminately and when [Syrian President Bashar al-]Assad has the right to determine who he’s going to bomb, because he can, quote, ‘Go after Nusra,’ but go after the opposition all at the same time because he wants to. You create a confusion that is impossible to separate out.”

“We need to get to the prohibition on flying,” Kerry said. “That would prevent Syria from doing what it has done so often in the past, which is to attack civilian targets with the excuse it was just going after Nusra.”

“To restore credibility to the process, we must move forward to immediately ground all aircraft flying in those key areas in order to de-escalate the situation and give a chance for humanitarian assistance to flow unimpeded,” he said.

When it signed the most recent cease-fire agreement, Kerry said, Russia said that Assad “would live by the cessation of hostilities and would accept the idea of not flying over agreed-upon areas.” Although Kerry did not specify, his proposal appeared to include grounding Russian aircraft in the area.

“Because of the last few days,” he said, “we have no choice but to do that sooner rather than later.”

Although Kerry offered no public details of the proposal, senior administration officials described it as a confidence-building measure that would prove Russian commitment and could get the cease-fire deal back on track. They said it could apply to all areas where the opposition is massed, including Aleppo, Idlib and as far south as the Damascus suburbs.

Kerry first proposed it in a private meeting with Lavrov Tuesday night. He also informed the Russians that, because of the convoy attack and the lack of secure humanitarian aid flows, conditions had not been met during the first week of the agreement to proceed to the second part of the deal, under which the United States and Russia would begin coordinated counterterrorism attacks.

Russia has given no initial response to the proposal, U.S. officials said. The International Syria Support Group, chaired by the United States and Russia, along with other outside actors in the conflict, including Iran, Saudi Arabia and Turkey, plans to meet again on Thursday.

Lavrov, who spoke before Kerry, did not respond to the grounding proposal, although Kerry first presented it to him in a private meeting Tuesday night.